Temperature-responsive circuit for load control apparatus

Abstract

A temperature-responsive circuit, for operation with a load-control apparatus having a control input for adjusting the magnitude of power applied to a load from a source, uses: a sensor responsive to the temperature in the vicinity of the load-control apparatus; a subcircuit for converting the temperature sensed by the sensor to the magnitude of an electrical parameter; a subcircuit for providing a reference electrical parameter having a magnitude predeterminately selected to equal the magnitude of the electrical parameter at a maximum desired temperature T 0 ; and a subcircuit for providing a control signal to the control input of the load-control apparatus responsive to a comparison between the electrical parameter and the reference electrical parameter, with the control signal having a magnitude respectively insufficient or sufficient to substantially affect the magnitude of power applied to the load if the magnitude of the electrical parameter is respectively less than or greater than the magnitude of the reference parameter. The load power is proportionally reduced if the magnitude of the electrical parameter exceeds the magnitude of the reference parameter. The gain of a comparator-amplifier may be selected to gradually decrease the power applied to the load to a preselected magnitude when a second temperature T 1 , greater than the maximum desired temperature T 0 established by the reference parameter, is sensed by the sensor.

What I claim is: 
     
       1. A temperature-responsive circuit, operating with a load-control apparatus having a control input at which is adjusted the magnitude of power applied to a load from a source and having an element providing a reference for the magnitude of load voltage, comprising: means for sensing the temperature in the vicinity of said load-control apparatus;   means for converting the temperature sensed by said sensing means to the magnitude of an electrical parameter;   means for providing a reference electrical parameter having a magnitude predeterminately selected to equal the magnitude of said electrical parameter at a maximum desired temperature To; and   means, having a selected gain, for providing a control signal to the control input of said load-control apparatus responsive to a comparison between said electrical parameter and said reference electrical parameter, said control signal having a magnitude respectively insufficient and sufficient to substantially affect and proportionally reduce the magnitude of power applied to said load if the magnitude of said electrical parameter is respectively less than and greater than the magnitude of said reference electrical parameter, and said gain is selected to gradually decrease the power applied to said load to a preselected minimum magnitude when a second temperature T 1 , greater than the desired temperature T O , is sensed by said sensing means; said control-signal-providing means also having an active semiconductor device connected to said load-control apparatus element and operative to reduce said load voltage as said sensed temperature is increased above said temperature T O .   
     
     
       2. The circuit of claim 1, wherein said sensing means is a thermistor. 
     
     
       3. The circuit of claim 2, wherein said converting means converts the resistance of said thermistor, responsive to sensed temperature, to the magnitude of an electrical voltage. 
     
     
       4. The circuit of claim 3, wherein said converting means includes: a source of operating potential; and at least one fixed resistance in an electrical series connected circuit with said thermistor between said operating potential source and a circuit common potential; the seriesconnected circuit having a node at which said voltage appears with a magnitude responsive to said sensed temperature. 
     
     
       5. The circuit of claim 4, wherein said reference electrical parameter is a reference voltage. 
     
     
       6. The circuit of claim 5, wherein said controlsignal providing means includes a single transistor. 
     
     
       7. The circuit of claim 6, wherein said reference voltage is the base-emitter voltage of said transistor. 
     
     
       8. The circuit of claim 5, wherein said reference voltage is the base-emitter voltage of a transistor. 
     
     
       9. The circuit of claim 3, wherein said reference electrical parameter is a reference voltage. 
     
     
       10. The circuit of claim 9, wherein said controlsignal providing means includes a single transistor. 
     
     
       11. The circuit of claim 10, wherein said reference voltage is the base-emitter voltage of said transistor. 
     
     
       12. The circuit of claim 1, wherein said element is a resistance and said reference is the voltage across said resistance; said active semiconductor device operating to shunt current around said reistance and reduce said reference voltage thereacross, when said sensed temperature exceeds temperature T O . 
     
     
       13. The circuit of claim 1, wherein said sensing means is at least one semiconductor junction. 
     
     
       14. The circuit of claim 13, wherein said converting means converts the voltage across said at least one junction, responsive to sensed temperature, to the magnitude of a voltage varying with respect to a substantially temperature stable potential. 
     
     
       15. The circuit of claim 14, wherein said sensing means further includes: at least one current source, each current source connected to cause a substantially constant current to flow through an associated different one of said at least one junctions. 
     
     
       16. The circuit of claim 15, wherein said reference electrical parameter is a reference voltage. 
     
     
       17. The circuit of claim 16, wherein said control-signal providing means includes a field-effect transistor and an amplifier with a fixed gain. 
     
     
       18. The circuit of claim 14, wherein said reference electrical parameter is a reference voltage. 
     
     
       19. The circuit of claim 18, wherein said control-signal providing means includes a field-effect transistor and an amplifier with a fixed gain.